Apparatus and method for initiating an electrical discharge



Oct. 31, 1961 A. c. DUCAT! 3,007,030

APPARATUS AND METHOD FOR INITIATING AN ELECTRICAL DISCHARGE 5 Sheets-Sheet 1 Filed Feb. 2, 1959 //5 J09 INVENTOR.

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Oct. 31, 1961 A. c. DUCATI 3,007,030

APPARATUS AND METHOD FOR INITIATING E AN ELECTRICAL DISCHARGE Filed Feb. 2, 1959 3 Sheets-Sheet 2 FIG- 5.

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D INVENTOR. 55 fiOQW/VO a. 006 777 United States Patent APPARATUS AND IVIETHOD FOR INITIATlNG AN ELECTRICAL DISCHARGE Adriano C. Ducati, Corona del Mar, Calif., assignor to Plasmadyne Corporation, Santa Ana, Califi, a corporation of California Filed Feb. 2, 1959, Ser. No. 790,692

20 Claims. (Cl. 219-121) This invention relates to a method and means for initiating an electrical discharge, particularly in a torch apparatus for generating high temperatures, and also relates to the torch apparatus itself. More specifically, the invention relates to an electrical plasma-jet torch and to a method of elfecting automatic starting thereof.

Electrical plasma-jet or plasma-flame torches, for example of the type described in co-pending patent application Serial No. 747,094, filed July 7, 1958, for Plasma Stream Apparatus and Methods, inventors G. M. Giannini and A. C. Ducati, now Patent No. 2,922,869 dated January 26, 1960, incorporate a nozzle electrode and a back electrode separated by a chamber into which gas is introduced. A high-current electric arc is initiated and maintained between the electrodes in the region of the nozzle opening, and serves to effect heating of the gas so that it emanates through the nozzle opening at high temperature and velocity. The initiation of the arc in such torches has previously been achieved in various ways including the impressing of a high-voltage or highfrequency power source across the electrodes to strike a pilot arc therebetween. Other arc-starting methods have included the insertion of a conductor, such as a graphite filament, between the electrodes and in electrical contact therewith. These and similar systems have, however, been deficient in one or more ways including the following: unsuitability for remote-control operation, unreliability, undue complexity, and high cost.

In view of the above and other factors relative to methods and apparatus for effecting arc initiation, it is an object of the present invention to provide a method and apparatus for starting an arc in a highly effective, efiicient and reliable manner which is readily susceptible of remote-control operation as well as precise control.

A further object is to provide high temperature-generating apparatus incorporating improved arc-starting means.

A further object is to provide a highly eflicient and reliable arc-starting device, in combination with means for supplying a precisely controlled quantity of electrical energy thereto.

A further object is to provide an electrical plasma-jet or plasma-flame torch incorporating novel automatic starting means which operate in a highly simple and reliable manner, and which may be incorporated with relatively low cost and a minimum of complexity.

A further object is to provide an arc-starting apparatus and device susceptible of extremely accurate control.

A further object is to provide an automatic starting system in which means are provided to increase power through the use of an auxiliary gas supply.

A further object is to provide automatic pressure increasing and decreasing means for an automatic starting apparatus.

Another object is to provide means for compensating for dilferences between the duration of the starting arc and the time required to initiate the main are between the nozzle and back electrodes of the torch.

These and other objects and advantages of the invention will be more fully set forth in the following specification and claims, considered in connection with the attached drawings to which they relate.

In the drawings:

3,007,030 Patented Oct. 31, 1961 FIGURE 1 is a schematic longitudinal sectional view illustrating an electrical plasma-jet or plasma-flame torch incorporating automatic starting means constructed in accordance with the present invention;

FIGURE 2 is a greatly enlarged fragmentary view of the explosion chamber portion of the apparatus shown in FIGURE 1;

FIGURE 3 is a schematic wiring diagram illustrating one form of circuit means for generating a spark dis charge in the explosion chamber;

FIGURE 4 is a schematic wiring diagram illustrating another form of circuit means for generating the spark, and including electromagnetic means for moving one of the sparking electrodes toward the other;

FIGURE 5 is a schematic diagram of another form of starting circuit;

FIGURE 6 is a longitudinal sectional view of another form of starter device;

FIGURE 7 is a view corresponding generally to FIG- URE 2 but illustrating auxiliary gas inlet means;

FIGURES 8 and 9 are schematic diagrams of additional circuit adapted to increase the operating time of the starting means; and

FIGURE 10 is a schematic diagram of an additional embodiment, incorporating means for selectively increasing and decreasing gas pressure.

Stated generally, the apparatus comprises means to define an explosion chamber and a main arc chamber, the latter chamber being conditioned for generation of a highcurrent electrical discharge therein. Means are provided to effect a spark discharge in the explosion chamber,

thereby causing the injection of high-temperature ionized gas at high velocity into the main arc chamber to effect are initiation. The last-named means includes capacitor means to supply a precisely controlled quantity of electricity to the starting device.

Referring specifically to the embodiment shown in FIG- URES 1 and 2 of the drawings, the invention is illustrated as incorporated in an electrical plasma-jet or plasmaflame to-rch 10 of the general type described in the abovecited application. The torch comprises a cup-shaped metal nozzle electrode 11 having a radial wall 12 the center of which is provided with a nozzle opening 13. A metal back electrode 14, shaped generally as a disc, is mounted axially in nozzle electrode 11 and in spaced relation from the radial wall 12 thereof. More particularly, the back electrode is illustrated as being connected by screws 16 to a metal base element 17. Both the back electrode and the base element are surrounded by suitable insulation means 18 which not only elfect insulation of the back electrode from the nozzle but also cooperate with a retaining ring 19 to maintain the electrodes in assembled relationship.

A generally tubular insert 21, formed of tungsten or other suitable refractory metal, is mounted in nozzle opening 12. The center portion of back electrode 14 is also provided with an insert 22 of tungsten or other refractory metal. Cooling chambers are provided to eifect cooling of the tungsten inserts 21 and 22 and are indicated schematically at 23 and 24. Such chambers are adapted to receive a continuous flow of water passed therethrough by means of suitable conduits 25 and 26.

An annular chamber 27 is defined between back elec trode 14 and the radial wall 12 of the nozzle electrode, coaxial with the nozzle opening 13. Such chamber is adapted to receive gas introduced therein through a con duit 28 and inlet opening 29. Conduit 28 is tangential to chamber 27, so that gas introduced through inlet opening 29 at relatively high velocity will flow vortically in the chamber 27 and then will flow out nozzle opening 13. Such flow is relatively free of shock and turbulence, due

to the presence of a rounded edge 31 at the inner end of insert 21.

A suitable power source 32 is connected by means of leads 33 and 34 to the nozzle and back electrodes, respectively. It follows that when the power source is applied an arc (the main arc) may be initiated between the inserts 21 and 22. This effects heating of the gas introduced through conduit 28 to a high temperature, and also effects ionization of such gas, so that hightemperature electrical plasma jets out through nozzle opening 13 at high velocity and temperature. The chamber 27, and also the communicating nozzle opening 13, may be described as the main arc chamber.

The electrical discharge between inserts 21 and 22 does not commence automatically upon application of power source 32, which has a low voltage, but instead must be initiated as previously indicated. According to the present invention, arc initiation is effected by providing an explosion chamber 36 which communicates through a relatively small-diameter port or passage 37 with the main arc chamber 27 and 13. Passage 37 should be so directed that high-temperature ionized gas emanating therefrom will fill the space between inserts 21 and 22 to eifect initiation of the main arc.

Means are provided to efiect a spark discharge in explosion chamber 36, and comprises an electrode rod 38 having a refractory tip 39 formed of tungsten or the like. Electrode 38 is illustrated (FIGURE 2) as being inserted through a bore 41 in base 17 and back electrode 14, and as being insulated by a sleeve 42 formed of heat-resistant insulating material. The inner end surface 42a of sleeve 42 is generally radial to tip 39, and forms one wall of the explosion chamber 36.

Referring next to schematic FIGURE 3, as well as FIGURE 2, there is illustrated one form of circuit means for generating a spark between tip 39 and an internal wall portion 36a (comprising a second electrode) of chamber 36. The circuit means may comprise a step-up transformer 43 energized from a suitable source 44 of alternating voltage, for example a standard 115 volt A.C. source. The secondary of transformer 43 is connected across a capacitor 46, there being a suitable rectifier 47 and switch 48 interposed between the transformer and capacitor so that the capacitor is charged by direct current when switch 48 is closed. A neon tube 49 and current-limiting resistor 51 are connected in series with each other across the capacitor 46 in order that the neon tube will light when the capacitor is substantially fully charged.

Capacitor 46 is connected through a lead 52 to electrode 38, and through a lead 53 to the base 17 and thus the back electrode 14. A switching device 54 of the spark-gap type is interposed in lead 52 to initiate discharge of the capacitor and thus effect generation of a spark between tip 39 and the wall portion 36a of the explosion chamber. More specifically, switching device 54 comprises two terminals 56 which are caused to move towards each other when a solenoid 57 is energized. Solenoid energization occurs upon closing of a switch 58 to cause flow of current from a suitable source indicated at 59. The terminals 56 are thus caused to move sulficiently close together that a discharge will take place therebetween, and this will elfect generation of a spark discharge in explosion chamber 36. Terminals 56 are initially much farther apart than the spacing between tip 39 and wall portion 36a.

Description of the method, particularly with relation to the embodiment of FIGURES 1-3 Stated generally, the method comprises conditioning an area or region for initiation of an electrical discharge, providing an explosion chamber in communication with such area or region, introducing gas into the explosion chamber, and generating a spark in the explosion chamber. The spark causes heating and ionization of the gas, so that the gas expands outwardly at high velocity and enters the above-mentioned area or region to initiate the discharge therein. In the showing of FIG- URES 1 and 2, the area or region 13 and 27 is conditioned for initiation of the discharge by applying the power source 32 through leads 33 and 34. Gas is introduced into the explosion chamber 36 through passage or port 37, and is heated upon creation of a spark between electrode tip 39 and the wall portion 36a of chamber 36. The resulting high-temperature ionized gas flows through passage 37 at high velocity and fills the space between inserts 21 and 22 so that the discharge is generated between such inserts to cause passage of a high-temperature plasma flame out nozzle opening 13.

With relatively specific reference to FIGURES 1-3, the method comprises rapidly introducing gas, preferably an inert gas such as argon, through conduit 28 and tangentially into chamber 27 for vertical flow therein and subsequent discharge out the nozzle opening 13. A portion of this gas enters the passage 37 and fills the explosion chamber 36. The power source 32 is then applied to maintain a potential difference between the nozzle and back electrodes, but such potential difierence is insufficiently great to effect ignition of the flame.

Thereafter, or previously, the capacitor 46 is charged through rectifier 47 from source 44 by closing the switch 48. Switch 48 is maintained closed until the lighting of neon tube 49 indicates that the capacitor is fully charged, after which the switch 48 is opened. Switch 58 is then closed to efi'ect energization of solenoid 57 from source 59, causing the terminals 56 to move sufficiently close together to effect a spark discharge therebetween. Capacitor 46 then discharges through terminals 56, leads 52 and 53, electrode 38 and tip 39 thereon, and the elements 17 and 14 which define the explosion chamber 36.

The resulting spark in explosion chamber 36 has sufficient power to cause rapid heating and expansion of the gas therein, as well as ionization of such gas. The heated and ionized gas flows at a high velocity through passage 37 into chamber 27 and nozzle opening 13. The presence of the heated and ionized gas causes initiation of the discharge between inserts 21 and 22, and this in turn causes heating of the gas from conduit 28 so that such gas streams out through nozzle opening 13 at high temperature and velocity.

When the gas is introduced through conduit 28 at sufficient pressure and velocity, the electric arc is constricted to the vortex in the whirling gas so that the current density of the arc, and thus the temperature thereof, are greatly increased to result in generation of a plasma flame having an extremely high temperature.

The following is a specific example of an automatic starting system which has been successfully employed in conjunction with a plasma torch of the general type shown in FIGURE 1. These values are not to be construed as limitations, but instead as examples of an operative system. The spacing between the adjacent ends of inserts 21 and 22 may be inch, and the voltage applied from source 32 may be 50 volts. The pressure of the argon gas entering chamber 27 may be 20 p.s.i. gauge. Explosion chamber 36 may have a diameter of inch, and the diameter of passage 37 may be .062 inch. The are gap between tip 39 and the wall portion 36a of chamber 36 may be .031 inch.

Capacitor 46 should be of the low-inductance type, and may have a capacitance of 2 mf. It may be charged to a voltage of 5000 volts.

Embodiment of FIGURE 4 FIGURE 4 corresponds to FIGURE 3 except that switching device 54 is omitted, and means are provided to effect movement of the electrode tip 39 toward the wall of chamber 36 to thus initiate the spark in the explosion chamber. Such means to move the tip 39 may comprise a core or armature 61 connected to electrode 38 and adapted to be shifted in response to energization of a solenoid 62. Solenoid 62 is connected to a current source 63 through a switch 64. The relationship between electrode 38 and insulating sleeve 42 is such that the electrode may slide in the sleeve in response to solenoid energization, without breaking the seal which prevents outflow of gas from explosion chamber 36 except through passage 37. Suitable means, not shown, are provided to retract the solenoid core 61 when the solenoid is deenergized. The retracted position of solenoid 61 is such that electrode tip 39 is spaced sufliciently far from the wall portion 36a of the explosion chamber that no sparking will occur upon charging of the capacitor 46.

In performing the method with the embodiment of FIGURE 4, capacitor 46 is again charged from source 44 by closing switch 48, and then opening switch 48 upon lighting of neon tube 49. Switch 64 is then closed to eifect solenoid energization, which causes the electrode 38 and its tip 39 to shiit to the right. At the instant that the extreme end of the electrode becomes sufficientl-y close to the wall portion 36a to permit generation of the spark, sparking occurs and the capacitor 46 discharges through the above-indicated circuit including leads 52 and 53, electrode 38, and torch portions 14 and 17.

The circuit of FIGURE 4 produces several advantages, one being that the spark-discharge energy is all concentrated in the explosion chamber 36. A second advantage is that erosion or wear of the end of electrode tip 39 does not afiect performance. Thus, it is not necessary to compensate for the effects of electrode wear and erosion. A further advantage of the embodiment of FIGURE 4 is that the arrangement compensates automatically for variations in gas pressure. Thus, an increase in the gas pressure means that the spark gap must bereduced for a predetermined capacitor voltage, but such gap reduction is effected automatically since the amount of movement of the electrode tip 39 is caused to be sufficient to provide for all normal values of gas pressures. Changes in voltage are likewise compensated for.

Since capacitor 46 is of the low-inductance type, and is preferably connected to the electrodes through lowinductance leads, the spark discharge is of short duration, on the order of a few microseconds or less. The discharge period is relatively short in comparison to the velocity of movement of the electrode in response to solenoid energization. It follows that the capacitor will discharge substantially completely while the electrode tip 39 travels only a very short distance. Thus, substantially the entire discharge in explosion chamber 36 takes place at optimum conditions when the spark has a maximum length. The result is that the power generated in the explosion chamber 36 is maximized. It is to be understood that the voltage in the spark is proportional to the length of the spark gap, but that the spark current is about the same for various lengths. It follows that the initiation of the spark at the earliest possible time, as tip 39 travels toward the wall of explosion chamber 36, results in generation of the maximum power in chamber 36 so that more plasma is produced therein than when the spark gap is shorter.

Embodiment of FIGURE 5 The embodiment of FIGURE 5 corresponds to that of FIGURE 3, except as will be specifically stated. Accordingly, similar components have been given the same reference numerals. In place of the switching device 54 of FIGURE 3, FIGURE 5 incorporates an ionization chamber 100 defined by a suitable envelope 101 formed of glass or the like. A pair of terminals 102 and 103 are interposed in lead 52, being suitably mounted within the chamber 100 in spaced relationship. An electrode 104 is provided in chamber 100, generally between terminals 102 and 103, and is connected through a lead 106 to a switch 107. Switch 107, in turn, is connected to one 6 end of the secondary 108 of transformer 43, the other end of such secondary being connected to the rectifier 47 previously indicated. In the present embodiment, lead 52 is tapped to an intermediate portion of secondary 108, instead of being connected to one end of the secondary as in the previous forms.

The chamber is filled with gas at a suitable relatively high pressure which prevents the initiation of a discharge between terminals 102 and 103, upon charging of capacitor 46, until a triggering potential is applied to electrode 104. Such potential is applied by closing switch 107, it being understood that the triggering potential is much greater than the potential between terminals 102 and 103 due to the fact that electrode 104 is connected to the extreme end of secondary 108 whereas terminal 102 is only tapped to an intermediate part thereof.

To briefly summarize the operation of the embodiment of FIGURE 5, the capacitor 46 is charged as in the previous embodiments, by closing switch 48 and then opening it as soon as the lighting of neon tube 49 indicates that full charging has been effected. It is then merely necessary to close the switch 107 and thus apply the triggering potential to electrode 104, which initiates the discharge between terminals 102 and 103 and completes the capacitor-discharging circuit from capacitor 46 to the electrode tip 39 within the explosion chamber 36.

Embodiment of FIGURE 6 FIGURE 6 illustrates a self-contained device adapted to be substituted for the electrode 3839, insulator 42, chamber 36 and port or passage 37 in the embodiment of FIGURES 1 and 2 as well as the circuits of FIGURES 35. The device is indicated generally at 109, and comprises a generally cylindrical metallic housing or casing 110. One radial end wall 111 of casing is centrally provided with a round opening 112 of predetermined diameter. In the indicated form, a peripheral portion of the housing is formed with threads 113 for threaded insertion into an apparatus wherein an arc is to be initiated.

An insulator element 116, composed of ceramic or the like, is provided within housing 110 and entirely fills the same except for an elongated cylindrical explosion chamber 117 which extends coaxially to opening 112 and is illustrated as having the same diameter. Chamber 117 and the opening 112 therefore form a continuous passage or chamber.

A conductor or electrode 118 is provided within insulator 116 and extends to the rear or inner end of the explosion chamber 117. Electrode 118 is suitably insulated by a rearwardly-extending outer portion 119 of the insulator 116, as well as by a sleeve 121 formed of a suitable heat-resistant insulating plastic.

It is to be understood that electrode 118 may be connected into any of the circuits of FIGURES 35 in place of the electrode 38, whereas casing or housing 110 may also be connected into any of the circuits of FIGURES 3-5 in place of electrode 14. Where the device 109 is connected into the circuit of FIGURE 4, electrode 118 is caused to be slidably mounted within the insulator 121 and the refractory 1 164419.

The explosion chamber 117 is filled with gas which enters the same through the opening 112, the latter communicating with the main arc chamber as in the case of port or passage 37 of FIGURE 2. Accordingly, when the discharge circuit from capacitor 46 is completed as described with relation to FIGURES 35, a spark is initiated between the tip of electrode 118 and the wall of nozzle opening 112. The result is that the gas in chamber 117 is instantaneously and efficiently heated and ionized, and fiows through the outlet opening 112 at high temperature and velocity to provide the desired arc-starting efiect.

An important advantage of the present devices and circuits resides in the fact that the quantity of electricity discharged through the explosion chamber may be accurately controlled, and the discharge may be very precisely timed. By precisely controlling the amount of electricity stored in capacitor 46, the temperature generated in the explosion chamber may be accurately regulated.

In the embodiment of FIGURE 6, the spark path is accurately controlled by the insulating wall of the explosion chamber 117, such explosion chamber being relatively long and narrow as indicated. This provides extremely efficient heating, and uniform electrode wear. Furthermore, the embodiment of FIGURE 6 is advantageous in that the unit is completely self-contained, having its own casing 110 which may be threaded into the desired apparatus after all initial adjustments and calibrations have been made at the factory. This is particularly true with relation to the embodiments of FIGURES 3 and 5, where the electrode 118 is rigidly maintained within the insulator 116-119.

The back electrode 14 of FIGURES 1 and 2 may be provided with a bore which corresponds generally in location and direction to the passage 37 but is sufficiently large to receive the casing 110. The inner end of such bore is appropriately internally threaded to receive the threads 113. The axis of explosion chamber 117 is therefore directed toward the region between inserts 21 and 22, so that the generation of a spark in chamber 117 causes outflow of hot ionized plasma to such region for initiation of the main discharge.

Embodiment FIGURE 7 FIGURE 7 corresponds to FIGURE 2, and has been given the same reference numerals. However, a gas inlet passage 130 is suitably formed through back electrode 14 and communicates with the explosion chamber 36. Passage 130 also communicates with a conduit 131 which should have a diameter at least as large as that of passage 130, and which extends to a suitable source 132 of a gas, such as argon, under substantial pressure which is higher than that within the central regions of chamber 27. A suitable valve 133 is interposed in the conduit 131 to control the flow of gas to the inlet 130 and thus to the explosion chamber.

In the operation of the embodiment of FIGURE 7, opening of the valve 133 effects flow of high-pressure gas from source 132 through the relatively large-diameter conduit 131 and inlet 130. Conduit 131 and inlet 130 are substantially larger than passage 37, so that the pressure in the explosion chamber 36 becomes much higher than that at the outlet end of passage 37. Because of this build up of pressure in chamber 36, a spark will not occur between electrode tip 39 and wall portion 36a until the voltage is substantially higher than in the situation where the only means of charging chamber 36 is through passage 37. It follows that the spark will be of higher power, with consequent outflow of more and higher-temperature plasma through passage 37 and into the chamber 27. It is to be understood that the valve 133 is only schematically indicated, and that it may be disposed very close to the chamber 36 and associated with suitable means to close the valve immediately prior to generation of the spark. The result is that substantially all of the generated plasma flows out through passage 37 instead of backfiring into inlet 130.

The embodiment of FIGURE 7 is particularly suitable for situations in which the main plasma torch is discharging into an evacuated chamber, such as a wind tunnel. In these cases, the pressure in chamber 27 is relatively low, so that the pressure in explosion chamber 36 would also be relatively low were it not for the presence of the auxiliary gas supply described above. It is to be understood that inlet 130 may be tangential to chamber 36, and that outlet 37 may be axial of electrode 38-39. The resulting vortical flow in chamber 36 results in a miniature plasma torch which corresponds generally to the main torch (including elements 28, 29 and 13).

Additional embodiments and components particularly adapted to compensate for difierences between the duration of the starting plasma and the time required to initiate the main arc The duration of the spark between electrode tip 39 and wall portion 36a in most of the previous embodiments (or between electrode 118 and the wall of opening 112 in the embodiment of FIGURE 6) is normally short, on the order of 10 microseconds. Thus, particularly in relatively large systems, such time may be shorter than the time required to initiate the main are between inserts 21 and 22 (FIGURE 1). Stated otherwise, it will be understood that if the plasma is only present between inserts 21 and 22 for a time period shorter than the time required for the main arc current build up, no main arc will result.

In view of the above factors, it is within the scope of the invention to bridge low-inductance capacitor 134 (FIGURE 1) between the main leads 33 and 34 to the nozzle and back electrodes. Capacitor 134 becomes charged upon application of power to leads 33 and 34, and will discharge between the inserts 21 and 22. as soon as plasma is injected therebetween from passage 37. Since capacitor 134 has a low inductance, it will discharge immediately upon injection of the plasma to efiect initiation of the main are, such main are then being continued due to steady flow of power from source 32. Switch means, not shown, may be provided to cut the capacitor out of the circuit as soon as the arc is started.

It is also within the scope of the invention to provide an inductor 135 (FIGURE 3) in the discharge circuit from capacitor 46 to electrode 38-39. The inductor 135 may also be incorporated in the circuit of FIGURE 5. The effect of the inductor is to decrease the rate of discharge of capacitor 46 and thereby greatly extend the duration of the are from electrode tip 39 to wall portion 36a. The result is the flow of a smaller or lower-power stream of plasma out passage 37, but for a much longer period of time which is adequate to effect initiation of the main are even in situations where the capacitor 134 (FIGURE 1) is not employed.

Referring next to FIGURE 8, this illustrates schematically a circuit which is analogous to the ones shown in FIGURES 3 and 5, similar components having been given the same reference numerals. However, in the embodiment of FIGURE 8 an additional and relatively small capacitor 138 is bridged between the leads 52 and 53 in the discharge circuit from the main or larger capacitor 46. Furthermore, a resistor 139 is interposed in lead 52, between the capacitors 46 and 138. The triggering devices of FIGURES 3 and 5 are replaced by the contacts 141 of a relay 142.

Relay 142 has an additional set of contacts 143 in the charging circuit for capacitor 46. The contacts 141 and 143 are suitably associated with each other so that the charging circuit for capacitor 46 will be open when the discharging circuit therefor is closed, and vice versa. Contacts 143 thus correspond to switch 48 in FIGURES 3 and 5. The relay is illustrated as having a coil 144 associated with a suitable source of power, indicated at 145, so that upon reverse energization of the coil the contacts 141 and 143 will shift between open and closed positions.

A resistor 146 is provided in the charging circuit for capacitor 46 in order to limit the initial surge of current thereto. Such a resistor 146 has also been shown in FIG- URES 3-5, inclusive, and serves the same purpose.

As previously indicated, capacitor 138 has a capacity much smaller than that of capacitor 46. For example, the capacity of capacitor 138 may be in the range of to A of that of capacitor 46. The size of capacitor 138 is increased when it is desired to decrease the frequency of spark repetition in the explosion chamber 36. Similarly, the size of resistor 139 is increased when it is desired to decrease the frequency of spark repetition.

In the operation of the embodiment of FIGURE 8, relay 142 is first shifted so that contacts 143 are closed to effect charging of capacitor 46 through the rectifier 47. When the lighting of neon tube 49 indicates that capacitor 46 is fully charged, the relay 142 is operated to open contacts 143 and close contacts 141. Capacitor 46 then discharges (partially) through resistor 139 and into the smaller capacitor 138. As soon as capacitor 138 becomes charged, it discharges through the electrodes in explosion chamber 36 to create a spark with consequent generation of plasma. When capacitor 138 is thus discharged, it is immediately recharged from capacitor 46, and again discharges through the explosion chamber. There may therefore, for example, be as many as a thousand or more rapidly repeated sparks in the explosion chamber 36, each spark having a discharge time on the order of ten microseconds, for example. The sparking continues until capacitor 46 becomes substantially discharged.

The arrangement is thus one in which a large number of rapidly repeated spark discharges are provided in the explosion chamber to effect flow of plasma into the space between inserts 21 and 22 (FIGURE 1) for a time period sufficient to insure initiation of the main arc therebetween. It is pointed out that this system effects relatively long-continued plasma generation without the necessity of increasing the power of power supply 44. It is also pointed out that the capacitor 46 will not discharge directly through the explosion chamber 36. This is because capacitor 138, when discharged, acts as a short or low-resistance shunt between leads 52 and 53 to prevent fiow of current directly from the capacitor 46 to the electrodes in the explosion chamber.

Referring next to the embodiment of FIGURE 9, a system is schematically illustrated for effecting long-continued sparking in the chamber 36 but with a power supply having greater power. Thus, a source 148 of alternating current, or in some instances pulsating direct current, is shown as connected to the primary 149 of a transformer 151, the transformer having a secondary 152 adapted to step up the voltage. Secondary 152 is connected through a resistor 153 to a capacitor 154, suitable leads 155 and 156 being provided for this purpose. Leads 155 and 156 also extend, respectively, to the electrode tip 39, and to elements 14 and 17 as in the previous embodiments.

The capacity of capacitor 154 should be relatively large when the frequency of source 148 is relatively low, such as 60 cycles. When the frequency of source 148 is increased to a higher value, the capacity of capacitor 154 may be made much smaller. Eventually, with increasing frequency, the capacitor 154 may be eliminated since the leads will then have suificient capacity for the desired purpose.

In the operation of the embodiment of FIGURE 9, each half cycle of the voltage wave from source 148 effects charging of capacitor 154 with one polarity, whereas the next half cycle effects charging thereof with the opposite polarity. Each time capacitor 154 is charged it will discharge through the circuit including the electrodes in the explosion chamber 36. It follows that the frequency of the discharges in the explosion chamber 36 will be twice the frequency of source 148. The discharges in the explosion chamber are, of course, continued as long as the power is applied, which may be sufficiently long to insure initiation of the main are between inserts 21 and 22 in FIGURE 1. It is preferred that the frequency of source 148 be relatively high, such as 1000 cycles per second.

10 Embodiment of FIGURE 10 FIGURE 10 illustrates schematically an additional embodiment in which means are provided for selectively increasing or reducing gas pressure in the explosion chamber, as required by the gas conditions within the main arc chamber 27 (FIGURE 1). The apparatus of FIG- URE 10 is particularly adapted to be employed in conjunction with the circuit of FIGURE 4, so that the gas pressure within the explosion chamber will be either maxi mum or minimum, as the case may be, at the instant a spark is generated in such chamber.

The apparatus is illustrated schematically to comprise an elongated cylinder 170, of relatively small internal diameter, having a forward end which is closed except for a small-diameter nozzle passage 171. It is to be understood that the cylinder is made of electrically-conductive material, and that it may form part of the elements 14 and 17 indicated in FIGURE 1. Thus, nozzle passage 171 may correspond to the previously-described passage 37.

The explosion chamber is indicated by the reference numeral 172, and is formed in advance of a piston 173 disposed in cylinder 170 and having a forward end wall 174. The explosion chamber thus constitutes the compression chamber Within cylinder 170.

Piston 173 is integral with an elongated piston rod 176 which extends axially of the explosion chamber 172 and has a relatively large-diameter piston 177 provided on the outer (left) end thereof. Piston 177 is slidably mounted in a cylinder 178, the latter being fixedly associated with a suitable support which is indicated schematically at 179. A suitable fluid-pressure source and control 181 is connected through conduits 182 and 183 to opposite ends of cylinder 178, the arrangement being such that operation of the source and control 181 will effect rapid movement of piston 177 between the extreme positions permitted by cylinder 178 and under control of an operator.

An additional cylinder 184, having a diameter substantially larger than that of the explosion chamber 172, is illustrated as being disposed between the small-diameter cylinder 170 and the cylinder 178. The chamber within the cylinder 1S4, numbered 185, has mounted therein a large-diameter piston 1 86. Piston 186 is formed on rod 176 at a location corresponding to that of piston 177, so that both are at the left ends of their respective cylinders when the piston 173 is relatively remote from the forward end of the cylinder 170 which defines the explosion chamber. Conversely, all of the cylinders move with the piston rod 176, to the right as viewed in the drawing, so that they are \all art the right ends of their respective cylinders at the same time.

The piston rod 176 and the various pistons may be integral with each other, and all may be formed of a suitable insulator such as Teflon. An electrode 187 is mounted axially of the piston rod and protrudes from both ends thereof as illustrated. The extreme forward end 188 of the electrode is so oriented with relation to the associated pistons that it will be disposed only a very slight distance from the forward end wall of the explosion chamber when the pistons 177 and 186 have reached the extreme limit of their forward travel. Electrode 187 may be connected to the lead 52 shown in FIGURE 4, whereas the cylinder 170 may be connected to the lead 53 of FIGURE 4. The solenoid elements 61 and 62 of FIGURE 4 are replaced, in the illustrated form of the present embodiment, by the piston 177 and cylinder 178.

The forward end portion of the electrode 187 protrudes from wall 174, so that such wall is spaced a predetermined distance from the foiward end wall of the explosion chamber when the parts are at their extreme forward positions. Such distance is sufiicient to afford continued communication between the explosion chamber and first and second conduits 189 and 190. Both of these conduits have substantially larger internal diameters than the nozzle passage 17 1, so that the flow of gas there- 1 1 through will provide instantaneous pressure changes within the explosion chamber due to the relatively slow flow of gas through the nozzle passage.

The first conduit 189 extends from the explosion cham ber to chamber 185 on the forward side of piston 186, so that forward movement of the piston 186 will result in a great increase the pressure within the explosion chamber. The second conduit 198 extends between the explosion chamber and chamber 185 on the rear side of piston 186, so that forward movement of the piston 186 effects drawing of gas out of the explosion chamber 172 to reduce the pressure therein.

Suitable valves 191 and 192 are mounted, respectively, in conduits 189 and 198, adjacent the explosion chamber, in order to control communication between such chamber and the chamber 185 on opposite sides of piston 186. Such valves are each adapted, when in one position, to vent the connected end of chamber 185 to atmosphere while at the same time blocking communication between the explosion chamber and either such connected end of chamber 185 or atmosphere. A suitable source 193 of gas under pressure is connected through a valve 194 to the conduit 189. Source 193 may contain the same gas as is introduced into the main arc chamber 27 (FIGURE 1), but at a considerably higher pressure than the pressure of gas in chamber 27 at the outlet end of nozzle passage 171.

Proceeding next to a description of the operation of the embodiment of FIGURE 10, let it first be assumed that it is desired to increase the pressure in the explosion chamber 172 immediately prior to generation of a spark therein, in order to increase the generated power as indicated with reference to the embodiment of FIGURE 7. It is pointed out that the present embodiment effects such increase with only a small amount of gas and for only a relatively short period of time. For such operation, valve 192 is turned to its position effecting communication between the ambient atmosphere and the end of chamber 185 on the rear side of piston 186, via conduit 190. At the same time, as previously indicated, communication between conduit 198 and the explosion chamber 172 is blocked by the valve 192. Valve 191, on the other hand, is turned to a position effecting communication between the explosion chamber 172 and the forward portion of chamber 185, forwardly of piston 186, there being no communication with the atmosphere.

If desired, the above-described valve settings may be maintained for a time period sufiicient to permit inflow of gas from chamber 27 through passage 171 until the pressure within chamber 172 and the forward portion of chamber 185 is approximately the same as that in chamber 27 at the outer end of passage 171. However, since the pressure in chamber 27 is relatively low in certain applications, as when the torch is being employed in a wind tunnel, the valve 194 may be opened to permit flow of relatively high-pressure gas from source 193 into chambers 185 and 172. For example, such source 193 may be at one atmosphere gauge pressure.

It is then merely necessary, after closing of valve 194 and after charging of capacitor 46 (FIGURE 4) as previously described, to operate the fluid-pressure source and control 181 in such manner as to effect rapid forward shifting of the piston rod 176, and all of the pistons, from the illustrated positions. This effects a great increase in the pressure within the explosion chamber 172 due to the forward movement of piston 173 to directly compress the gas in such chamber, and due to the forward movement of the much larger-diameter piston 186 to compress the gas in the forward end of chamber 185, which latter gas is transmitted through conduit 189 to the explosion chamber.

At approximately the same time that the pistons reach the extreme forward ends of their strokes, the front end 188 of the electrode will come sufficiently close to the front end wall of cylinder 17 to permit a spark to be generated therebetween. Such sparking will occur, as previously de- 12. scribed in detail, at the optimum moment for producing the maximum power in the explosion chamber. The exact distance between the electrode end 188 and the end wall of the explosion chamber, at the time of sparking, will depend upon factors such as the voltage on the capacitor, gas pressure, etc., as previously described.

During the above-described forward travel of piston 186, air is drawn into the end of chamber on the rear side of piston 186 through conduit i and valve 192. This prevents the formation of a vacuum in such chamber end to reduce the power of the piston stroke.

There exist situations in which the pressure in the main arc chamber 27 is very high, even higher than is desired within the explosion chamber 172. For operation under such conditions, valve 192 is turned to a position blocking the vent to atmosphere and affording communication between the explosion chamber and the end of chamber 185 on the rear side of piston 186. Valve 194 is maintained closed, and valve 191 is turned to a position blocking communication between conduit 189 and chamher 172 but effecting communication between conduit 189 and the atmosphere. Such valve settings are not made, however, until pressure source and control 181 has been operated to shift the pistons back to the positions illustrated in the drawing.

Assuming that the capacitor 46 has again been charged as described with reference to FIGURE 4, the pressure and control 181 is again operated to effect shifting of the piston rod 176 and associated pistons to the right. Gas is then drawn rapidly from the explosion chamber 172 through conduit 190 to the end of chamber 185 on the left of piston 186, creating a substantial vacuum in the explosion chamber. Because the piston 186 is much larger in diameter than the explosion chamber, such drawing off of gas more than offsets the tendency of the piston 173 to increase the gas pressure in the explosion chamber. As the piston 186 moves to the right, the gas forwardly thereof in chamber 185 is vented to atmosphere through conduit 189 and valve 191 to prevent an undesirable build up of pressure therein.

As soon as the electrode end 188 becomes sufficiently close to the end wall of chamber 172, sparking will occur as previously stated. Such sparking occurs when the gas pressure in chamber 172 approaches minimum, since the pistons are then very near the right ends of their strokes. The gas pressure in the explosion chamber during the instant of sparking is thus reduced to a desirable value calculated to effect optimum flow of plasma through passage 171 into the space between inserts 21 and 22 (FIG- URE l) for initiation of the main arc therebetween.

Various embodiments of the present invention, in addition to what has been illustrated and described in detail, may be employed without departing from the scope of the accompanying claims.

I claim:

1. An electrical torch, which comprises a nozzle member having a nozzle opening therein, a back electrode, means to define a chamber between said nozzle and said back electrode and communicating with said nozzle opening, means to introduce gas into said chamber for outflow through said nozzle opening, means to maintain an electric arc to said back electrode in said chamber and in the region of said nozzle opening, means to define a relatively small chamber adjacent said first-mentioned chamber and communicating therewith, and means to generate an electrical discharge in said last-mentioned chamber to cause heating and ionization of the gas therein for flow into said first-mentioned chamber to initiate said arc.

2. An electrical plasma-flame torch incorporating automatic starting means, which comprises a nozzle electrode, a back electrode, means to define a gas-pressure chamber between said electrodes and communicating with the nozzle opening in said nozzle electrode, means to introduce oxidation-preventing gas into said gas-pressure chamber for expansion through said nozzle opening, means to define a relatively small explosion chamber adjacent said gas-pressure chamber, means to effect communication between said explosion chamber and said gas-pressure chamber and serving to eflect charging of said explosion chamber with said gas from said gas-pressure chamber, electrode means provided in said explosion chamber, and means to efi'ect generation of a spark to said electrode means in said explosion chamber and having sufficient power to heat said gas charge in said explosion chamber to a relatively high temperature and to efiect ionization thereof, whereby said heated and ionized gas passes into said gas-pressure chamber to initiate an electric are between said nozzle and back electrodes.

3. The invention as claimed in claim 2, in which said last-named means includes a capacitor, means to charge said capacitor with a predetermined quantity of electricity, and circuit means to effect discharge of said capacitor through said electrode means in said explosion chamher.

4. An electrical plasma-jet torch, which comprises a nozzle electrode having. a nozzle opening formed therein, a back electrode spaced and insulated from said nozzle electrode, means to define an annular gas-pressure chamber between said electrodes coaxial and communicating with said nozzle opening, means to introduce non-oxidizing gas tangentially into said gas-pressure chamber for vortical fiow therein and subsequent expansion through said nozzle opening, means to define an explosion chamber adjacent the arcing portion of said back electrode, outlet means efiecting communication between said explosion chamber and said gas-pressure chamber and directed generally toward the space between said arcing portion of said back electrode and said nozzle opening, a starting electrode having an end portion disposed in said explosion chamber, a capacitor, and means to discharge said capacitor through a circuit including a spark from said end portion of said starting electrode to thereby generate hot ionized gas in said explosion chamber for high-velocity flow through said outlet means into said space in order to initiate an electric are between said nozzle electrode and said back electrode, said electric arc being disposed in the vortex in said whirling gas and serving to convert a portion of said whirling gas into hightemperature plasma for discharge at high velocity through said nozzle opening.

5. The invention as claimed in claim 4, in which said circuit includes spaced terminals disposed remote from said explosion chamber, and means to move said terminals toward each other to eflect arcing therebet-ween.

6. The invention as claimed in claim 4, in which said means to discharge said capacitor include means to move said end portion of said starting electrode toward another electrode connected in said circuit, until said end portion is sufiiciently close to said other electrode to efiect sparking therebet-ween due to the voltage on said capacitor.

7. The invention as claimed in claim 4, in which said means to discharge said capacitor include a pair of spaced terminals disposed remote from said explosion chamber and connected in said circuit, envelope means to define an ionization chamber and enclosing said terminals, a trigger electrode mounted in said ionization chamber, and means to apply to said trigger electrode a voltage sufiicient to initiate a discharge between said terminals.

8. The invention as claimed in claim 4, in which said explosion chamber is elongated and has generally the same diameter as said outlet means, in which said end portion of said starting electrode is remote from said outlet means, in which the wall of said explosion chamber is formed of insulating material, and in which at least a portion of said outlet means comprises an additional electrode connected in said circuit for sparking to said end portion of said starting electrode.

9. The invention as claimed in claim 4, in which said explosion chamber is at least partially defined by a wall portion of said back electrode, in which said outlet means comprises a relatively small-diameter passage extending between said explosion and gas-pressure chambers, and in which said back electrode is connected in said circuit and is insulated from said starting electrode.

10. A method of starting an electrical plasma-jet torch having a nozzle electrode and a back electrode and an arc space therebetween, which comprises applying a voltage across said electrodes, providing an explosion chamber in communication with said arc space and adapted to receive gas therefrom, introducing non-oxidizing gas into said are space to thereby charge said explosion chamber, and creating a spark discharge in said explosion chamber to thereby heat and ionize the charge therein and efiect flow of the resulting hot ionized gas into said are space between said electrodes for initiation of arcing therebetween.

11. An electric arc apparatus incorporating automatic starting means, which comprises first and second spaced electrodes adapted to maintain a main arc therebetween, first circuit means to supply power to said electrodes for generation of said main arc, means to inject ionized gas between said first and second electrodes for initiation of said main arc, said last-named means including starting electrode means to generate said ionized gas, second circuit means to supply power to said starting electrode means, and means to effect correlation between said first circuit means and said second circuit means to insure that said ionized gas is inserted into the space between said first and second electrodes for a time period sufficient to efiect initiation of said main arc.

12. The invention as claimed in claim 11, in which said correlation means includes low-inductance capacitor means connected in said first circuit means.

13. The invention as claimed in claim 11 in which said correlation means includes inductor means provided in said second circuit means.

14. An electric arc apparatus, comprising first and second main electrodes adapted to have a main arc struck therebetween, means to define a plasma-generation chamber having outlet means directed toward the vicinity of the space between said first and second main electrodes, starting electrode means to generate an arc in said plasma-generation chamber to thereby heat gas in such chamber for discharge through said outlet means to said space, and means independent of said outlet means for introducing gas at relatively high pressure into said plasma-generation chamber to thereby increase the amount of electrical power required for maintenance of said are in said plasma-generation chamber with consequent increase in the power of the plasma transmitted out said outlet means and into said space between said main electrodes.

15. The invention as claimed in claim 14, in which additional means are provided to introduce gas at relatively low pressure into the space between said main electrodes, and in which said means for introducing gas into said plasma-generation chamber is larger in cross-sectional area than said outlet means whereby relatively high-pressure gas introduced into said plasma-generation chamber eifects build up of gas pressure therein to a substantially higher pressure than that of said gas between said main electrodes.

16. In an electrical torch apparatus having two main electrodes adapted to have an electric arc maintained therebetween, automatic starting apparatus comprising a first and relatively large-capacity capacitor means, a sec 0nd and relatively small-capacity capacitor means, means to charge said first capacitor means, circuit means to effect discharge of said first capacitor means into said second capacitor means, starting electrode means adapted to generate sparks in an explosion chamber to thereby effect introduction of high-temperature ionized gas into the space between the main electrodes, and circuit means to effect discharge of said second capacitor through said starting electrode means, whereby said second capacitor means repetitively charges from said first capacitor means and then discharges through said starting electrode means to provide a series of rapidly-repeated sparks at said starting electrode means.

17. In combination with an electric torch apparatus having main electrodes adapted to maintain a main electric arc therebetween, starting means comprising starting electrode means to generate an arc in a chamber to thereby effect flow of ionized gas through an outlet from said chamber into the space between said main electrodes, capacitor means connected to said starting electrode means for discharge therethrough, and supply means to supply alternating voltage to said capacitor means to thereby charge the same with opposite polarities upon each half cycle with consequent generation of sparks at said starting electrode means and at twice the frequency of said supply means,

18. An electric arc torch apparatus, which comprises main electrode means adapted to have an electric are established thereto in a predetermined space, means to define an explosion chamber, passage means for eflecting communication between said explosion chamber and said space, starting electrode means mounted in said explosion chamber, means to impress a predetermined relatively high voltage between said starting electrode means and additional electrode means disposed relatively adjacent said passage means, means to effect movement of said starting electrode means towards said additional electrode means for initiation of a discharge therebetween in said explosion chamber upon approach of said starting electrode means into proximity with said additional electrode means, and movable wall means operably associated with said starting electrode means for substantially simultaneous movement and adapted to effect predetermined pressure variation in said explosion chamber at a rate substantially greater than the rate of pressure equalization due to flow between said explosion chamber and said space through said passage means, whereby the pressure in said explosion chamber is caused to be substantially different from the pressure insaid space at the instant of sparking between said starting electrode means and said additional electrode means.

19. An electrical plasma-jet torch apparatus, which comprises a nozzle, a back electrode, means to efiect flow of gas into the space between said nozzle and said back electrode and thence out through the nozzle opening in said nozzle, means to define a relatively smalldiameter explosion chamber having an elongated cylindrical shape and having a substantially closed end which communicates through a small-diameter passage with said space between said nozzle and said back electrode in the vicinity of said nozzle opening, a first piston mounted in said explosion chamber for longitudinal movement therein, starting electrode means mounted in said first piston for movement in said explosion chamber from a position remote from said small-diameter passage to a position closely adjacent the same, capacitor means connected to said starting electrode means for discharge through said explosion chamber upon approach of said starting electrode means to the vicinity of said smalldiameter passage, a cylinder, a second piston slidably mounted in said cylinder and having a diameter substantially larger than that of said explosion chamber, communication means to effect communication between said cylinder and said explosion chamber, and means to effect conjoint movement of said pistons in the same direction to efiect compression of the gas in said explosion chamber to a relatively high pressure at the instant that said starting electrode means approaches sufiiciently close to said small-diameter passage to efiYect an electrical discharge.

20. The invention as claimed in claim 19 in which means are provided to effect communication between said explosion chamber and said second cylinder on the side of said second piston opposite the point of connection between said second cylinder and said first-mentioned communication means, and in which valve means are provided in said communication means to determine the direction of pressure variation in said explosion chamber due to movement of said second piston.

References Cited in the file of this patent UNITED STATES PATENTS 2,010,920 Karsel Aug. 13, 1935 2,034,756 Hansell Mar. 24, 1936 2,105,344 Campbell Jan. 11, 1938 2,508,954 Latour et al. May 23, 1950 2,516,016 Pakala July 18, 1950 2,646,492 Ballard July 21, 1953 2,768,279 Rava Oct. 23, 1956 

